1. Field of the Invention
The present invention relates to a communication apparatus such as a facsimile machine, a communication method, and a program, and more particularly, to a facsimile machine having a capability of facsimile transmission according to the ITU-T recommendation V.17.
2. Description of the Related Art
In the art of communication apparatus, a facsimile machine or the like is known which has a capability of facsimile communication according to the ITU-T recommendation V.17. In the facsimile communication according to the ITU-T recommendation V.17, when a long training/TCF signal is received, training information (correction value by means of training) is fixed (hereinafter, referred to as “frozen”), while, during an operation of receiving a short training/picture signal, training information is frozen each time a carrier of a picture signal is detected.
Even when training information is frozen, if a modem is set into a mode in which a short training/picture signal is received, training information is adaptively updated.
However, when facsimile communication is performed by using a particular modem, if an echo is generated in a communication line having a delay, an echo of a CFR signal (according to the ITU-T recommendation V.21) transmitted from a receiving facsimile machine is received by the receiving facsimile machine. The receiving facsimile machine incorrectly recognizes the received echo signal as a carrier of a picture signal and adjusts training data on the basis of the echo of the CFR signal. In this case, even if a correct short training/picture signal arrives thereafter, the receiving facsimile machine cannot receive it (more precisely, the received signal cannot be correctly demodulated).
The above problem is described in further detail below with reference to FIGS. 10 and 11. When a high-speed signal (picture signal) is not found (cannot be correctly demodulated), one possible operation which may occur in a receiving facsimile machine is, as shown in FIG. 10, timeout of a T2 timer according to the ITU-T recommendation T.30. In this case, the receiving facsimile machine terminates the current communication. FIG. 11 shows another possible operation. In this example, when a picture signal is not correctly received, if a receiving facsimile machine finds PPS-Q, the receiving facsimile machine transmits PPR to request retransmission of the picture signal.